ring units, based on the entire polymer, and the polymer has a weight average molecular weight of 3,000 to 100,000. [0035] In a further preferred embodiment, the resin (A) is a polymer comprising recurring units of the following general formula (2a???): [0036] wherein R4 is hydrogen or methyl, R5 is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms, R6 is an acid labile group, R6a